Recently I added an auto power-down function to my FT-5.Its purpose is to shut the internal power down completely at the end of a print so that I can start a lengthly print and more or less walk away.In addition, I have changed the bed heater to a mains-powered silicone heater with an SSR to control it.This is much, much better than the original DC-powered one in many regards, but does pose a problem.The new heater is powerful enough to easily and quickly get up to dangerous temperatures if allowed to run away.So operating the printer unattended is not acceptable without some form of independent safety circuit.In addition, power glitches and brief outages are disgustingly common in our area and once the power has been lost I do not want the printer powering itself up again when the mains return. Whatever was printing at the time will be ruined anyway.

Please take a look at the attached writeup.It describes the modification in great detail including the circuit, the reasoning, the installation, the firmware changes and the parts used.Automatic power down.pdf (445.3 KB)

The .stl files for the printed components I created for the project are as follows-ClipWithSide_stout.stl (43.5 KB)RelayBoxShort.stl (534.7 KB)SwitchCover.stl (185.7 KB)ESwitchPanelwithLED_23OCT17.stl (771.4 KB)These may or may not be useful for anyone else's printer, but I thought I'd pass them along. Please note that they typically have to be scaled up 10x in the slicer because my CAD software refuses to output in mm format, only cm format.

The auto-power-down function is really nice to have and it all worked on the very first try (including the firmware mods).The added safety functions are good for peace of mind.

Thanks! I will save them in that scaled format for future reference.I have Blender but have not become comfortable with it yet.

When printing these things I used ABS for the clips (so that they would stay somewhat flexible) and PLA for everything else.I printed with a 0.6 nozzle and 0.25 layer heights (oops, I said 0.15, it was actually 0.25).You will probably need to use brims and supports for everything but the clips.All the parts except the clips were post-print finished with primer/surfacer paint and then wet sanded. Then they were painted with semi-gloss black paint.The clips were used as-printed.

Could you give a rough BOM cost break down, or possibly a rough total cost estimate for the whole project, assuming someone would be starting from scratch and not having many of the components on hand?This is really intriguing, and likely something I may want to integrate in the future. I currently don't run my printer unattended, for lack of any other reason than it just doesn't feel right. At least right now, in its stock configuration. Thanks,Dave

You can definitely use a less expensive main relay.I opted to use a DPDT high current plug-in version with an integral indicator light.You can use pretty much any SPDT or SPST-NO relay with the appropriate coil voltage and contact rating. They are out there at around $7.50 if you look around.The secondary relay is not that expensive to begin with, but less expensive ones can be had.

As for the switches, remember that I happened to have these laying around from another project, so my cost was actually $0.You can use any common normally open pushbutton for the on switch, any common normally closed pushbutton for the off switch and any common rocker or toggle switch for the override switch.As long as their contacts can handle the current and voltage of course.You can probably get by for less than $10-$12 total for them.That would bring the cost down to around $38.

I would be willing to create a version of the switch housing that has round holes (or no holes) rather than square ones if anyone needs that.Then more common (and less expensive) panel-mount switches could be used.

Ron,Thank you for the detailed response!One more question -do you have any time delay from when the print finishes to when the machine powers down? If not, have you had any issues with heat creep into your hot end causing problems for your next print?

Yes, effectively I have a short delay of sorts at the end.This was done by making the shutdown code (M81) the very last line of the "end of print" gcodes.The codes that precede it home the XY motion, lower the Z from wherever the print ended, retract the filament somewhat, shut off the bed and hot end heaters and shut off the steppers.Then when the M81 is executed the PSU will carry over for a second or so after the relay cuts out.But a specifically added gcode delay? Not really.

As for heat creep and filament management, that is an excellent point.I retract the filament a fair distance as part of the end gcodes.Currently I think it is set at 10 mm. I really haven't had any problems except if I want to change out the filament spools after it has cooled down completely (such as between PLA and ABS which I do all the time).It makes a slight plug that doesn't want to pull back through the inlet of the E3D very well.But that is just a leftover from the stock heater block days that I forgot about when converting to the Volcano block (my bad).I could quite easily increase it to something more like 50 mm to get the filament completely out of the E3D heat sink and the problem would go away.I saw something on YouTube the other day where someone mentioned retracting it 100 mm at the end of the print for much the same reason.Perhaps I'll try that.

When the next print is being set up I always manually "prime" the nozzle anyway and run a skirt or brim at the start, so it really makes no difference how far it was retracted at the end of the previous print.It might as well be 100 mm.

But problems with baking the filament and that sort of thing? Not really anything that I have noticed thusfar.

I'm still trying to read through the schematic of the auto power down. Electronics is not my strongest talent.

One thing I don't get is, the 10 Amp SSR, you have the load coming out of the bottom switch out spot. and what I would assume be neutral going over to the 110V heater. However, the lower wire on the heater is already labeled N. Could you explain what is going on here?Thanks,Dave

But you can find them domestically if you don't want to wait for shipping.The one that you show will work perfectly.I wouldn't feel safe without having them personally.And as you notice I used two of them, one for either side of the heated plate, so that they will be redundant and also could sense a hot spot if one happened toward a side.

Actually, the lower connection to the switched output side of the SSR is "line" and is an input to the SSR from the switched mains shared connection to the power on button and relay.The output connection from the SSR is the upper connection as shown and goes directly to the bed heater. It has no name per-se.The lower wire on the heater is "neutral". and is continually connected to the mains through the power entry module.You always want to break or control the "line" side, not the neutral because the neutral is connected to ground somewhere in the building typically.At least in 110 volt mains applications such as North America.

In 220 volt countries there is a bit less of a clear choice, but if either side is earthed or connected to some neutral-like point, that would be the side you would not break.